If we move closer to an object while still being able to focus, then we can see it in more detail. As we approach the object, it occupies a bigger angle.
As the person approaches the object in the diagram above the angular siz increases from
to
The angular magnification is
This is not the same as the linear magnification. To illustrate this difference, consider the diagram below.
The linear magnification is
This is approximately equal to the angular magnification, with the approximation being better with decreasing